This invention relates generally to expandable intraluminal vascular grafts, commonly referred to as stents, and more particularly concerns the coating of metal stents with polymer materials capable of carrying and releasing therapeutic drugs.
Stents are implanted within vessels in an effort to maintain the patency thereof by preventing collapse and/or by impeding restenosis. Implantation of a stent is typically accomplished by mounting the stent on the expandable portion of a balloon catheter, maneuvering the catheter through the vasculature so as to position the stent at the desired location within the body lumen, and inflating the balloon to expand the stent so as to engage the lumen wall. The stent automatically locks into its expanded configuration allowing the balloon to be deflated and the catheter removed to complete the implantation procedure.
It is often desirable to provide localized pharmacological treatment of a vessel at the site being supported by the stent and it has been found convenient to utilize the stent as a delivery vehicle for such purpose. However, because of the mechanical strength that is required to properly support vessel walls, stents must typically be constructed of metallic materials which are not capable of carrying and releasing drugs. Various polymers on the other hand are quite capable of carrying and releasing drugs but generally do not have the requisite mechanical strength. A previously devised solution to such dilemma has been the coating of a stent's metallic structure with a polymer material in order to provide a stent capable of both supporting adequate mechanical loads as well as delivering drugs.
Various approaches have previously been used to join polymers to metallic stents including dipping, spraying and conforming processes. However, such methods have failed to provide an economically viable method of applying a very even coating of polymer on the stent surfaces or the ability to economically apply different thicknesses or different polymers in different areas on the same stent.
The prior art has been unable to overcome such shortcomings and a new approach is needed for effectively and economically applying a polymeric material to a metallic stent with a high degree of precision.